Sear locking device for automatic firearms



Sept 2l, 1954 c. H. CLEVELAND ErAL sEAR LOCKING DEVICE FOR AUTOMATICFIREARMS Filed Dee. 15, 195o l 'Fig-,ih

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Patented Sept. 21, 1954 UNITED SEAR LOCKING DEVICE Fon AUTOMATICFresenius Application December l5, 1950, Serial No. 201,054

F si

2 Claims. (C1. Sil- 149) (Granted under Title 35, U. S. Code (1952),

sec. 266) The invention described in the specication and claims may bemanufactured and used by or for the Government for governmental purposeswithout the payment to us of any royalty thereon.

This invention relates to means for preventing the premature release ofthe ring member of an automatic firearm and is particularly directed toan improved device for positively locking a sear against such movementas would permit the accidental release of a firing member therefromprior to the locking of a reciprocating bolt in battery position.

In automatic firearms of the type disclosed in Patent No. 1,628,226 toJohn M. Browning, there is provided a spring-biased firing memberslidably mounted in a reciprocable bolt for longitudinal movementbetween a cocked and a ring position. The firing member is retained inthe cocked position by the engagement thereof with a spring-biased Searslidably mounted in the bolt for vertical reciprocal movement therein.When the sear is depressed by suitable means, the firing member isreleased therefrom and moves forwardly under the bias of its spring todischarge a chambered cartridge. During the ensuing recoil movement ofthe bolt, a cooking lever pivotally mounted therein is rotated to forcethe firing member rearwardly into re-engagement with the scar which inthe meantime has been returned from its depressed position by the biasof its spring. During counter-recoil movement of the bolt, the cookinglever is rotated out of the path of movement of the firing memberwhereupon the latter is free to move forwardly upon release by the searand effect another cycle of operation.

While the foregoing arrangement is extremely simple and efficient, thefact that the scar rests directly upon the free end of a coil springintroduces the possibility that the vibration and impact forces.encountered during the automatic operation of the rearm may causesufficient movement of the sear to permit premature release of thevfiring member therefrom. If such accidental release occurs after thecooking lever has been rotated out of the path of movement of the firingmember but prior to the locking of the bolt in battery position, theconsequent premature discharge of the cartridge could effect seriousinjury not only to the lirearm itself but also to any personnel in theimmediate vicinity thereof. On the other hand, should such accidentalrelease occur while a portion of the cocking lever is still in the pathof movement of the ring member, the normal striking power thereof willbe reduced to the point where no ignition of the cartridge primer willresult. This type of firearm malfunction is commonly referred to in theart as a light blow and has caused considerable difficulty in thecontinuous function of the Browning type machine guns herewith concernedsince the bolt must be actuated to re-cock the firing member beforeoperation of the gun can be again resumed.

Various attempts have heretofore been made to lock the sear againstaccidental movement prior to the locking of the bolt in batteryposition. However, none of the suggested devices or mechanisms haveproven entirely satisfactory from a practical standpoint due to theirinconsistency of operation. Furthermore, some of these prior art deviceshave either required excessive modification of the gun or have added anundesirable number of new components thereto.

One of such prior art devices consists of a locking member pivotallymounted in the bolt by means of a vertical pin and arranged to belaterally cammed by the cooking lever into and out of engagement with atransverse notch provided in the side of the sear. A spring-biaseddetent is also required to engage the front end of the Sear lockingmember in order to prevent accidental movement thereof.V lhile suchdevice offers several worthwhile features, it also introduces otherproblems which the present invention has been specically designed toovercome.

For example, motion picture records and other exhaustive testing hasindicated that comparatively heavy impact forces are encountered whenthe rear end of the bolt strikes the buffer in the back plate of thefirearm receiver at the conclusion of recoil. Similar impact forces arealso present during counter-recoil when a shoulder on the underside ofthe bolt strikes the claws of an accelerator member. In fact, it hasbeen found that in some cases these impact forces are so severe that aspring-biased detent of the type found in the above-mentioned prior artdevice is ineffective in preventing such accidental movement thereof aswould permit premature unlocking of the sear.

Furthermore, with the sear locking device of the prior art, the timingrelationship between the vertical movement of the Sear and the pivotalscar-engaging movement of the lock member is extremely critical. Whenthe cooking lever begins to cam the forward end of the lock memberoutwardly relative to the Sear, the sear notch must be in exactalignment with the rear end of the lock member. However, since theupward movement of the sear is readily affected by such factors as thetension in the sear spring, the speed of bolt recoil, and the shockproduced by the above-mentioned impact forces, the consequent erraticmovement of the sear obviously fails to produce the desired alignment inevery cycle of operation. As a result, breakage of parts leading tofrequent stoppages of;A fire can, be expected or, at best, the cornersof the sear notch will be seriously mutilated in a relatively briefinterval of firearm operation.

Still another unsatisfactory feature of the prior art device lies in thepivotal type of movement utilized for the sear lock member. In thenecessity for keeping the number of firearm parts to a minimum, thecooking lever pin was used to retain the pivot pin of the sear lockmember. As a result, the fulcrum point of the lock member was locatednearer to the rear end thereof than to the front end. Thus, as thecooking lever cammed the front end of the lock member outwardly, therelative slower movement of the rear end served to increase the periodof time in which the sear remained unlocked thereby permitting thepossible misalignment of the notch therein with the engaging end of thelock member due to the factors previously mentioned.

Accordingly, it is an object of this invention to provide an improvedmeans for locking the scar of an automatic firearm in order to preventthe release of a firing member therefrom until after the bolt hasreached a fully locked battery position.

It is a further object of this invention to provide in an automaticfirearm bolt a slidable self -retaining lock member for preventing thepremature release of a firing member from a sear prior to the locking ofthe bolt in battery position.

Another object of this invention is to include in mechanism for lockinga reciprocable sear against prematurely releasing a firing membertherefrom an improved means for facilita-ting positive engagement of thelock with the sear despite the variations existing between each cycle ofsear movement.

It is still another object of this invention to provide in an automaticmachine gun of the Browning type a slidable lock member for preventingpremature release of the firing member from the sear wherein the lock isarranged to be self-retained in the bolt.

It is a particular object of this invention to provide an improved searlocking device for an automatic machine gun of the Browning type whereinsuch device comprises a single member requiring but a minimum ofmodification of the existing gun parts.

The specific nature of the invention as well as other objects andadvantages thereof will clearly appear from the following description ofa preferred embodiment as shown in the accompanying drawing in which:

Fig. 1 is a cross-sectional view taken along the line I-I of Fig. 2 toshow the cooperation of the sear, ring member, cooking lever, and searlock member;

Fig. 2 is a rear end view of the firearm bolt in which the elements ofFig. 1 are incorporated;

Fig. 3 is a fragmentary cross-sectional view taken along the line 3.-3of Fig. 2 which shows particularly well the manner in which the rear endof the sear lock member engages the notch in the sear;

Fig. 4 is a cross-sectional view taken along the iine lfd of Fig. 2 andshowing the lock member disengaged from the sear;

Fig. 5 is a cross-sectional view similar to Fig. l but showing the lockmember engaged with the sear;

Fig. 6 is a side view of the sear lock member of this invention; and

Fig. 7 is a cross-sectionalV View taken along the line I-T-'I of Fig. 5.

There is illustrated in Fig. 1 a bolt I2 of the well-known Browning typehaving a longitudinal hole I3 therethrough arranged to accommodate aspring-biased reciprooable firing member Ifl. A vertically disposed searI5 is slidably mounted in the rear end of bolt I2 and is normally biasedupwardly by a coil spring I6 into position to engage the rear end offiring member Ill. Accordingly, sear I5 serves to hold firing member Illin the cocked position. When bolt I2 goes into battery, sear I5 isdepressed by suitable means (not shown) and firing member Ill isreleased to move forwardly under its spring tension and initiate anothercycle of operation. A cooking lever Il is pivotally mounted in bolt I2about a transverse axis so that the lower end of such lever projectsinto a longitudinal slot I8 (Fig. l) in ring member lli. Thus, as boltI2 recoils, cocking lever is pivoted in a counter-clockwise direction bysuitable mechanism (not shown) so that the lower end thereof abuts therear end wall of slot I8 and thereby forces firing member Ill rearwardlyinto engagement with scar I5. Upon counter-recoil movement of bolt I2,cooking lever Il is pivoted in a clockwise direction so that the lowerportieri thereof will not interefere with the firing movement of memberIll. A longitudinal recess I9 is provided in the top of bolt i2 topermit the above-described movements of cooking lever I1.

The foregoing describes conventional structure which is more fullyexplained in the aforementioned Patent No. 1,628,226. However, aspreviously mentioned, there are occasions where scar I5 may beaccidentally depressed before bolt I2 reaches battery position therebyleading either to the premature firing ofthe gun or to a stoppageproduced by a light blow of firing member Ill on the primer of acartridge.

To avoid these specic malfunctions, the present invention proposes theaddition of a novel sear locking member 2t requiring but slightmodifications to existing firearm parts. One of these modifications isthe provision of a notch 2| angularly formed into one side of sear I5 asbest shown in Fig. 3. The second modification is the addition of alongitudinal slot 22 extending forwardly from the rear end of bolt I2and arranged to communicate with recess I9. Sear lock 20 is arranged tobe slidably mounted in slot 22 and essentially comprises a substantiallyrectangular body portion having a central bowed section 23 therein ofreduced thickness relative to the rest of lock 2G. A pair-of oppositelydisposed lugs 24 and 25 project outwardly from the side of lock 29 for apurpose to be explained. Lug 24 is provided with an upwardly andforwardly extending inclined surface 2S while lug 25 has a similar butoppositely inclined surface 2l thereon. Extending rearwardly from thebody portion of lock member 20 is a relatively narrow portion 28 havingan offset lug 29 at the rear end thereof which projects outwardly in thesame direction as lugs 24 and 25. Lug 29 is provided with an upwardlyand rearwardly inclined surface 39. A longitudinal rib 3i projectsupwardlyv from narrow portion 28 and is so located thereon that theinner side of such rib 3l serves toincrease the bearing surface areabetween lug 2Q and the rear end of the body portion of lock member 2t.The height of the rear portion of bolt slot 22 is increased as shown at32 in Fig. 7 in order to provide access for Sear lock rib 3 I.

It will be noted that the normal vertical distance from the top surfaceof bowed section 23 to the bottom surface of the remainder of lock 20 isgreater than the vertical distance between the Walls of slot 22.Accordingly, when lock 20 is assembled therein with lugs 24 and 25projecting into bolt recess I9, bowed section 23 is compressed by thewalls of slot 22 into a substantially linear plane. As a result, lockmember 20 is resiliently retained in bolt slot 22 and yet is free toreciprocate therein when suicient force is applied thereto as will behereinafter explained.

At the instant the rearm is discharged, eccking lever Il lies in theposition shown in Fig. 1. The recoil movement of bolt I2 serves to pivotcooking lever Il in a counter-clockwise direction as viewed in Fig. 1whereupon the lower end thereof cams firing member I4 rearwardly. Whenthe hook end of firing member I2 has moved past the mating hook portionof Sear I5, the arm of cooking lever` II strikes inclined surface 26 onlug 24 with sufficient force to overcome the resilient engagementbetween lock member bowed section 23 and the walls of bolt slot 22. Theresulting forward movement of lock member 29 continues until therearward travel of firing member I4 is halted upon contact of the rearend thereof with the front face of sear I5. During this overtravel offiring member I2 relative to sear I5, lug 29 of sear lock member 2S hasentered into scar notch 2| to positively look sear I5 against verticaldownward movement. In the event sear notch 2I is not precisely alignedwith lug 29 at the instant of locking due to the erratic sear movementhereinbefore discussed, inclined surface 30 of lug 29 will contact theoppositely inclined underside of the upper wall of sear notch 2 I andthereby cam sear I5 upwardly to the extent required for complete lockingthereof. The increased surface area formed by the inner side of rib 3|bears fully against the side of sear I5 immediately above angular searnotch 2l and thus prevents the excessive wear thereon which would resultif lock member contacted only the triangular portion formed by the upperwall of sear notch 2|.

Upon counter-recoil of bolt I2, cooking lever Il is pivoted in aclockwise direction as viewed in Fig. 1 and consequently strikesinclined surface .i of lug thereby forcing lock member 20 rearwardly.Thus, as bolt I2 moves into battery position, the continued rearwardmovement of scar lock 2c brings lug 29 thereon completely out ofengagement with sear notch 2l and frees sear I5 for the downwardvertical movement necessary to release firing member I4. This rearwardsliding movement of sear look 20 is halted when bolt I0 reaches theposition wherein no further pivotal movement is imparted to cookinglever Il. It will be noted that the force with which cooking lever ilstrikes lugs 24 and 25 is substantially cushioned by the resiliency ofSear lock 20.

From the foregoing description it is readily apparent to those skilledin the art that there is here provided a simple yet highly successfulmeans for positively looking the sear of a Browning type machine gun forthe purpose of preventing premature release of a ring member from suchsear. The reciprocable sliding movement of the sear lock member assuresan extremely rapid locking and unlocking movement which is particularlyeffective in prolonged the period of time in which the sear can belocked against accidental vertical movement. Furthermore, theself-retaining feature of the sear lock member eliminates the necessityfor introducing any additional detent means for securing the look tosafely resist any accidental movement which might be induced by theexcessive vibration and impact forces encountered in the automaticoperation of the gun. Moreover, due to the camming action between theupper wall surface of the sear notch and the inclined surface on thelooking lug of the sear, positive locking of the sear is assured despitethe erratic vertical movement imparted thereto by the spring arrangementfound in the Browning type machine guns. Finally, inasmuch as thepresent invention introduces but one new firearm component and only twoslight modifications to existing components, it can readily be seen thatthe incorporation thereof in the regular manufacture of the guns or themodication of existing guns would be a relatively simple and inexpensiveprocedure.

claim:

l. In an automatic firearm, a longitudinally reciprocable bolt arrangedfor movement between a reooiled and a counter-reooiled position, aspring-biased firing member slidably mounted in said bolt forlongitudinal movement between a cocked and a fired position, a cookinglever mounted in said bolt for reciprocating pivotal movement in a planeparallel to the plane of bolt movement, said cooking lever arranged toactuate said firing member into cocked position, said bolt having alongitudinal slot therein extending forwardly from the rear end thereofand disposed adjacent to and parallel with the path of movement of saidcooking lever, a spring-biased sear slidabiy mounted at the rear end ofsaid bolt for vertical movement into and out of engagement with saidfiring member, said scar having an angular notch in one side thereofcommunicating with said bolt slot when said sear lies in position toengage said firing member, and a longitudinal slidable memberfrictionally mounted in said bolt slot, said member comprising arelatively thin body portion having a pair of spaced-apart aligned lugsprojecting outwardly therefrom into the path of movement of said cookinglever, and a narrow rearwardly extending portion having an offset lug atthe terminal end thereof, said offset lug being arranged to engage insaid angular notch in said sear as said cooking lever strikes theforemost of said outwardly projecting lugs and actuates said slidablemember forwardly whereby said sear is locked against premature releaseof said firing member, said offset lug being also arranged to withdrawfrom said sear notch as said cooking lever strikes the rearmost of saidprojecting lugs and actuates said slidable member rearwardly wherebysaid sear is unlocked to permit release of said firing member therefrom.

2. The combination defined in claim 1 including an inclined cam surfaceon said offset lug operative on the upper angular wall surface of saidsear notch for camming said Sear upwardly in the event of incompletealignment of said offset lug with said sear notch.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 946,999 Hardy Jan. 18, 1910 1,375,451 Fowler Apr. 19, 19211,803,349 Pfeiffer May 5, 1931 2,462,114 Lochhead Feb. 22, 19402,427,304 Robbins Sept. 9, 1947 2,491,534 Taber Dec. 20, 1949

